Groundwater quality index and potential human health risk assessment of heavy metals in water: A case study of Calabar metropolis, Nigeria

Abstract

The study aims to determine the spatial variability of physico-chemical characteristics and heavy metals constituent of groundwater within Calabar Metropolis, as well as the potential human health risk of adults and children to heavy metals through ingestion and dermal pathways. Fifty groundwater samples were collected from different locations and analyzed for pH, total dissolved solids, temperature, electrical conductivity, Zinc, Chromium, and iron following standard methods. The variables were subjected to principal axis factoring analysis, hierarchical cluster analysis, and geospatial analysis. The water quality index of the study area was determined using the weighted average water quality index (WAWQI) method while the potential health risk was assessed in accordance with the USEPA approach. The average concentrations of Cr, Fe, and Zn were 0.02 mg/l, 0.05 mg/l, and 0.22 mg/l, respectively. The results of the factor analysis revealed that the contamination from dissolved solids were probably from geogenic sources. The comparison of the results with the WHO standard revealed that the permissible limits for EC and Cr in drinking water were exceeded in 2 % and 4 % of the locations, respectively. The water quality of the study area ranges within four categories: “good” to “very poor”. The order of toxicity of heavy metals based on mean concentration and total hazard quotient s (HQs) for both adults and children was as follows Zn > Fe > Cr. The total mean HQs for adults and children, for Cr, Zn and Fe were obtained as 4.63E-01, 2.10E + 01, 2.06E + 00 and 1.62E + 00, 7.35E + 01, 7.21E + 00, respectively. The hazard index values obtained from the human health risk analysis for both adults and children revealed that the heavy metals (HMs) had a significant contribution to non-carcinogenic risk (HI > 1) due to exposure to groundwater from the study area. Children were more at risk compared to adults (mean HIchildren = 8.24E + 01 > mean HIadult = 2.35E + 01). The lifetime cancer risk due to Cr was significant for both adults and children (mean LTCRadult = 3.47*10-1 > 10-6, mean LTCRchildren = 1.22 > 10-6). The range of water quality rating calls for concern and immediate action.